Employee Charles Gregory said he felt the floor rumbling as the blast erupted.

"It was real scary," he told the Associated Press news agency. "Have you ever heard the thunder real loud? It was like 10 times that."

Thick clouds of black smoke rose into the air as firefighters struggled to douse the flames.

The aftermath of the blast left a gaping hole in the earth, while chunks of charred metal littered the ground. Cars parked nearby were coated with a layer of ash.

One man who had remained unaccounted for was confirmed dead on Thursday afternoon, bringing the death toll to 15.

The Texas City refinery, 35 miles (55km) south-east of Houston, is the third biggest in the US, employing 2,000 people.

It processes roughly 450,000 barrels of crude oil each day, amounting to about 3% of domestic oil supply in the US and one-third of BP's output across the country.

'Sonic boom'

BP spokesman Bill Stephens said investigators had started looking into the cause of the explosion.

"We're going to be very thorough on this one," he said. "I can't tell you exactly when we will finish this investigation, but no stone will go unturned."

Investigators are poring over the wreckage

Another company spokesman, Hugh Depland, virtually ruled out terrorism as a factor.

He was backed by an FBI spokesman, who said agents had pulled out of the plant on Thursday.

Health officials said more than 70 of those injured had been working inside the refinery and some of them were in a critical condition.

Texas City was the scene of the country's worst industrial accident in April 1947, when a ship full of ammonium nitrate, used in fertiliser, exploded in the harbour, killing at least 576 people.

Were you in the area when the explosion occurred?

This debate is now closed. Thank you for your comments

My wife and I were at home about 10 minutes drive from the refinery. We heard a loud noise like thunder. First we thought it might be from the housing construction site in our area. When she turned on the TV to the news channel, there it was on the Breaking News. She promptly called the hospital she works and was called to duty at the Emergency Room. It was very terrifying. I am yet to find what happened to our Church building which is directly opposite the refinery. Bernice & Samuel Nkansah-Adjei, Texas City, TX, USA

A good friend of mine works there (she was not injured but was very, very frightened). This is a safety issue and NOT terrorists; why is every little ripple a terrorist act? However, these oil companies are not held accountable enough for unequivocally making certain employees and residents are protected. Baddi Singh, The Woodlands, Texas, USA

I have family in Texas City, we have been in contact with them throughout the day. They told us there was a huge explosion that vibrated through the air and ground knocking the pictures off the walls and breaking some of the windows in their neighbourhood. They stated that they were initially advised to remain indoors but this was soon lifted and as most of the injured were people living in the town there is a sense of loss throughout the town.Arthur Claxton, Elmwood USA/Ramsgate UK